1. Field of the Invention
The present invention relates to an image sensor and a fabricating method thereof, and more particularly, to a back side illumination (BSI) image sensor and a fabricating method thereof.
2. Description of the Prior Art
Please refer to FIG. 1. FIG. 1 shows a cross-sectional view of a conventional front side illumination (FSI) image sensor 100. As shown in FIG. 1, the FSI image sensor 100 comprises: a carrier board 110, a substrate 120, a pixel region 130, an interlayer insulating layer 140, metal lines 150, an isolation layer 160, and a bond wire 170. The light collection path must pass through the interlayer insulating layer 140 and the metal lines 150, which reflect the light and makes quantum efficiency worse. The circuit routing also blocks the light so the fill factor is limited, especially when photo diode area becomes smaller in advanced technology.
Please refer to FIG. 2. FIG. 2 shows a cross-sectional view of a conventional back side illumination (BSI) image sensor 200. As shown in FIG. 2, the BSI image sensor 200 comprises: a carrier board 210, a substrate 220, a pixel region 230, an interlayer insulating layer 240, metal lines 250, an isolation layer 260, and a bond wire 270. The light collection path passes through the substrate 220, and thus the BSI image sensor 200 can achieve higher fill factor because no circuit routing blocks the light. The quantum efficiency may not be good enough if the substrate 220 is thick, and thus a traditional solution is using a polish process to make the substrate 220 thin. However, the polish process costs higher and spends more time, and it is not easy to exactly control the stop timing of the polish process. Additionally, the isolation layer 260 of a special shell package type must be used as a contact interface to the carrier board 210 since the substrate 220 is thin. The isolation layer 260 of the special shell package type and the bond wire 270 cause waste of die area.